For purifying gaseous mixtures e.g. natural gas and flue gas, separating undesired components from the main stream can in some cases be achieved based on the relative size of the components (size-sieving). Sometimes better results can be achieved by making use of the properties of the components to be separated. For example, U.S. Pat. No. 4,963,165 describes the separation of polar from non-polar components using membranes made from polyamide-polyether block copolymers which do not appear to be crosslinked. Polyethylene oxide (PEO) based membranes have been described as suitable for separating CO2 from hydrogen and methane (Lin et al., Macromolecules, Vol. 38, no. 20, 2005, 8394-8407). JP8024602A and JP8024603A describe gas separation membranes containing a polyalkylene glycol di(meth)acrylate having 1-24 alkylene glycol repeating units. Hirayama et al, Journal of Membrane Science, 160, (1999), 87-99, describe polymer films made from polyethylene glycol mono- and di-methacrylates and their application for gas separation. JP7060079 describes plasma treated films having a hydrophilic surface comprising oxyethylene groups preferably having 2-30 repeating units. U.S. Pat. No. 5,069,926 describes porous ultrafiltration membranes suitable for the separation of oil and water which have been surface modified with plasma- or ozone-treated polyethylene glycol diacrylates. WO-A-2005/097304 describes membrane stacks comprising macroporous gel-filled membranes wherein polyethylene glycol diacrylates are used as cross-linkers.
There is a need for membranes having high permeability and selectivity for desired gases that are strong and flexible. Ideally such membranes can be produced efficiently at high speeds using toxicologically acceptable liquids (particularly water) in the composition. In this manner the membranes of the present invention can be made in a particularly cost effective manner. This invention aims at achieving these targets, at least in part.